(a) Field of the Invention
The present invention relates to an organic electroluminescent (EL) device having an excellent luminescence property such as high efficient luminance
(b) Description of the Related Art
An organic electroluminescent device (which will hereinafter be called xe2x80x9corganic EL devicexe2x80x9d) is a light-emitting device which makes use of the principle that when an electric is field is applied, a fluorescent material emits light in response to the charge recombination of holes injected from an anode and electrons injected from a cathode. After C. W. Tang et al. of Eastman Kodak Company reported a low-voltage-driven organic EL device using a double layered structure (C. W. Tang, S. A. Vanslyke, Applied Physics Letters, 51,913(1987) and the like), studies on an organic EL device have been briskly carried out. Tang et al. reported an organic EL device using tris(8-hydroxyquinolinol aluminum) in a light-emitting layer and a triphenyldiamine derivative to a hole-transporting layer. This stacked structure gives such advantages as an improvement in the injection efficiency of holes into the light-emitting layer; blocking of electrons injected from a cathode, which increase the efficiency of exciton production from charge recombination; and confinement of the excitons into the light-emitting layer. A double layered structure composed of a hole-injecting and transporting layer and an electron-transporting and light-emitting layer or a triple layered structure composed of a hole-injecting and transporting layer, a light-emitting layer and an electron-injecting and transporting layer is well known as an organic EL device. In order to increase the recombination efficiency of injected holes and electrons, various improvements in the device structure or fabrication process have been introduced to such multi-layered devices. As a hole-transporting material, triphenylamine derivatives such as 4,4xe2x80x2,4xe2x80x3-tris(3-methylphenylphenylamino)triphenylamine and aromatic diamine derivatives such as N,Nxe2x80x2-diphenyl-N,Nxe2x80x2-bis(3-methylphenyl)-[1,1xe2x80x2-biphenyl]-4,4xe2x80x2-diamine, which are starburst molecules, are well known (e.g., Japanese Patent Application Laid-Open Nos. 20771/1996, 40995/1996, 40997/1996, 543397/1996. and 87122/1996).
As an electron-transporting material, oxadiazole derivatives, triazole derivatives and the like are well known.
As a light-emitting material, known are chelate complexes such as tris(8-quinolinolate)aluminum complex, coumarin derivatives, tetraphenylbutadiene derivatives, bisstyrylarylene derivatives, oxadiazole derivatives and the like. Since various color light in a visible region from blue to red are obtained from these light-emitting materials, there increased expectation for industrialization of a full color organic EL device (e.g., Japanese Patent Application Laid-Open Nos. 239655/1996, 138561/1995, 200289/1991 and the like).
In recent days, organic EL devices with high brightness and long lifetime have been disclosed or reported, but any of then are not enough in these properties.
It is therefore an object of the present invention to provide materials for the organic EL devices having high luminance or long-term operating life.
The inventors found that specific organic compounds having a triphenylene frame exhibit excellent properties for high-luminance electroluminescence, and thus are suitable for the materials for the organic EL devices In addition, among other organic compounds having the triphenylene frame, the compounds having a diarylamino group as a substituent group, wherein the aryl group has a styryl group as a substituent group, provided excellent organic EL devices exhibiting an especially high luminance.
In accordance with the above findings, the present invention provides organic EL devices defined as follows:
(a) Organic EL device having one or more than one organic thin-film layers disposed between an anode and a cathode, and at least one of the organic thin-film layers including, in the form of a mixture or a single substance, the trphenylene compound expressed general formula [1] as follows: 
wherein each of R1 to R12 independently represents hydrogen atom, halogen atom, hydroxyl group, substituted or non-substituted amino group, nitro group, cyano group, substituted or non-substituted alkyl group, substituted or non-substituted or non-substituted alkenyl group, substituted or non-substituted cycloalkyl group, substituted or non-substituted alkoxy group, substituted or non-substituted aromatic hydrocarbon, substituted or non-substituted aromatic heterocyclic group, substituted or non-substituted aralkyl group, substituted or non-substituted aryloxy group, substituted or non-substituted alkoxycarbonyl group, or carboxyl group, and wherein each of R1 to R12 may be a ring formed by two of the atoms or groups as mentioned herein;
(b) Organic EL device defined in (a), wherein the triphenylene compound defined by formula [1] (simply referred to as triphenylene compound [1], hereinafter) is such that at least one of R1 to R12 is a diarylamino group expressed by xe2x80x94NAr1Ar2, each of given Ar1 and Ar2 independently representing aryl group having 6-20 carbons, at least one of Ar1 and Ar2 having a substituted or non-substituted styryl group as a substituent group;
(c) Organic EL device defined in (a), wherein the organic thin-film layer includes a hole transport layer having the triphenylene compound [1] in the form of a mixture or a single substance;
(d) Organic EL device defined in (a), wherein the organic thin-film layer includes at least a hole transport layer having the triphenylene compound defined [1] in a mixture or a single substance, and wherein at least one of R1 to R12 is a diarylamino group expressed by xe2x80x94NAr1Ar2, each of given Ar1 and Ar2 independently representing aryl group having 6-20 carbons, at least one of Ar1 and Ar2 having a substituted or non-substituted styryl group as a substituent group;
(e) Organic EL device defined in (a), wherein the organic thin-film layer includes at least an electron transport layer including the triphenylene compound [1] in the form of a mixture or a single substance;
(f) Organic EL device defined in (a), wherein the organic thin-film layer includes at least an electron transport layer having the triphenylene compound [1] in the form of a mixture or a single substance, and wherein the triphenylene compound [1] is such that at least one of R1 to R12 is a diarylamino group expressed by xe2x80x94NAr1Ar2, each of given Ar1 and Ar2 independently representing an aryl group having 6-20 carbons, at least one of Ar1 and Ar2 having a substituted or non-substituted styryl group as a substituent group;
(g) Organic EL device having a organic luminescent zone disposed between an anode and a cathode, wherein the organic luminescent zone includes, adjacent to said anode, one or more than one organic thin-film layers, at least one of said one or more than one organic luminescent layers including a compound expressed in a general formula [1]; and
(h) Organic EL device defined in (g), wherein the triphenylene compound defined by formula [1] (simply referred to as triphenylene compound [1], hereinafter) is such that at least one of R1 to R12 is a diarylamino group expressed by xe2x80x94NAr1Ar2, each of given Ar1 and Ar2 independently representing aryl group having 6-20 carbons, at least one of Ar1 and Ar2 having a substituted or non-substituted styryl group as a substituent group.
The EL device according to the present invention exhibits a high luminance and a long-term operating life compared to the conventional EL device.
The above and other objects, features and advantages of the present invention will be more apparent from the following description, referring to the accompanying drawings.